1. Field of the Invention
The present invention relates generally to power over Ethernet (PoE) systems and methods and, more particularly, to a system and method for integrated temperature measurement in PoE applications.
2. Introduction
The IEEE 802.3af and 802.3at PoE specifications provide a framework for delivery of power from power sourcing equipment (PSE) to a powered device (PD) over Ethernet cabling. Various types of PDs exist, including voice over IP (VoIP) phones, wireless LAN access points, Bluetooth access points, network cameras, computing devices, etc.
In the PoE process, a valid device detection is first performed. This detection process identifies whether or not it is connected to a valid device to ensure that power is not applied to non-PoE capable devices. After a valid PD is discovered, the PSE can optionally perform a power classification. In a conventional 802.3af allocation, each PD would initially be assigned a 15.4 W power classification after a Layer 1 discovery process. An optional classification process could then reclassify the PD to a lower power level. For example, a Layer 2 classification engine can be used to reclassify the PD. In general, a Layer 2 classification process can be included in PoE systems such as 802.3af, 802.3at or proprietary schemes. The completion of the power classification process enables the PSE to manage the power that is delivered to the various PDs connected to the PSE system.
In general, PoE is a relatively new application that is being applied to an existing cabling infrastructure. Significantly, this cabling infrastructure was not originally designed for the distribution of power. Accordingly, the provision of power over the cabling infrastructure can be impacted by the presence of heat, which reduces the capacity of the cable to transmit power and data.
Heat can be present due to a variety of sources. For example, heat can be present in the ambient environment or can be generated through the transmission of current in the cable itself or in surrounding cables. PoE systems must account for this heat during operation. These considerations will play an even greater role in the administration of high-power PoE systems such as that proposed by the IEEE 802.3at specification. What is needed therefore is a mechanism that enables the PoE system to account for the existence of heat in an active manner during system operation.